Investment casting is a well-known and mature technology for precise replication of an existing object or model. Generally speaking an original wax model or a wax model made from an impression of an object is mounted on a sprue base extending from an end cap (gasket). A casting flask is secured to the gasket to form a container having an open upper end, and wet investment plaster is poured into the flask to a level above the model. The assembly is then set aside to dry and cure. Thereafter, the flask assembly is heated in an oven to drive off the wax and create the hollow casting mold cavity. A liquid casting material is then poured into the cavity through the sprue vent, and permitted to solidify to form an exact replica of the original model. In the case of molten metal casting, the molten metal is poured into the cavity while the investment is hot, so that the metal will fill all the mold voids and displace all the gas therefrom before it solidifies.
Production and transportation of investment plaster is costly, due to the energy intensive nature of investment plaster manufacturing and the density of the resulting product. Handling of dry investment plaster is a health and safety problem, as the fine particulate plaster poses a respiratory risk. Disposal of used investment is messy and ecologically wasteful, and has a negative environmental impact.
Porosity in cast parts is another shortcoming that occurs in investment casting. Porous parts are less strong, less aesthetic, and in many cases require additional finishing. Many porous parts are not usable at all.
A persistent problem in casting is that the investment plaster must be dry before being heated in the oven. When flasks containing investment that is still damp are placed into a kiln, the outside of the plaster cast heats and dries first, due to the fact that only the end surfaces of the flask assembly are exposed. The inner portion of the investment remains damp, while the drying of the outer end portions seals in the moisture. As the mold heats and the moisture turns to steam, the resulting internal steam pressure may cause the flask to explode. The mold is ruined, and a great deal of time and material is wasted. If the model is a primary wax pattern, the destruction of the original object represents a loss of many hours of highly skilled labor, and the original cannot be exactly duplicated.
Moreover, the investment casting process requires sufficient time to complete the steps of investment, drying, burnout, casting, and finishing. Often the process requires at least two days to complete, and this turnaround time for the flasks and models necessitates a large inventory of flasks, gaskets, and models for high volume, continuous production. The extensive time required to complete the entire process is problematic in terms of work schedules and delivery times. In addition, the prodigious amount of energy consumed in running a kiln, especially at its highest temperatures, is expensive and causes deterioration of the kiln element and lining.